var pieces = [];
 var puzzleNode;
 var nextNode;
function sramblePieces() {
 pieces = document.getElementById('puzzleContainer').getChildNodes();
 pieces.sort( function() {return 0.5 - Math.random()} );
 puzzleNode = document.getElementById('puzzleContainer').getFirstChild().getId();
 for(i=0; i < pieces.length; i++) {
   oldNode = document.getElementById(puzzleNode);
   newNode = document.getElementById(pieces[i].getId());
   document.getElementById('puzzleContainer').replaceChild(oldNode, newNode);
   puzzleNode = document.getElementById(puzzleNode).getNextSibling().getId();
 }
}